1. Field of the Invention
The present invention generally relates to a scintillation camera apparatus, and more particularly to an autotuning circuit for automatically controlling the high voltage applied to a photomultiplier and the output characteristics of the photomultiplier.
2. Description of the Prior Art
In a scintillation camera apparatus as one of the medical diagnostic imaging apparatuses, to adjust the high voltage applied to a photomultiplier, an operator sets an object in a predetermined position with respect to a scintillation camera, and then manually adjusts the high voltage while observing the positional relationship between a spectrum displayed on a monitor television and a window displayed thereon. In a scintillation camera apparatus operable with a computer, the CPU of the computer processes the spectrum to be displayed in a multichannel and automatically recognizes the peak value of the spectrum. The CPU controls the stepping motor interlocked with a potentiometer for fine adjustment of high voltage, on the basis of a deviation of the peak value from a target value. In this way, the peak value of the spectrum can be automatically tracked.
The output of the photomultiplier of each channel is controlled with manual adjustment of a potentiometer, which is coupled in series between the cathode of each photomultiplier and ground. Alternatively, the output of the preamplifier of each photomultiplier is automatically controlled by an attenuator with a feedback system.
The manual adjustment of the high voltage supply causes a complicated and time-consuming work, and is a lack of qualitatively precise controlling. The adjustment using the stepping motor arrangement requires a large and expensive apparatus which is also poor in durability.
With controlling the preamplifier output, a control circuit cannot be accommodated within the photomultiplier or its socket. This results in an increase in the size of the preamplifier.
An object of this invention is to provide a scintillation camera apparatus with an arrangement which is small in size, good in durability, reliability and cost performance, and further with an autotuning means capable of automatically setting the high voltage and output of a photomultiplier.